Hello, I have an external hard drive which has several damaged sectors due to a fall while operating. The hard drive itself is still working but the inner NTFS partition is quite damaged, cannot be mount under Windows nor Linux; chkdsk recognizes it as a NTFS partition but is not able to fix its metadata because it is unable to write in some sectors. So I thought on using Drive Image to create an image (ignoring read errors) and then mounting it read-write and trying to fix the metadata structures so that I could recover some of the data in there, but I didn't find anything to mount it read-write.

No, the image cannot be mounted in R-Drive Image as a read-write disk, only as a read-only one.
But I suggest you do that another way. You create an image in R-Studio which fills bad sectors with a predefined pattern, then open the image in R-Studio, when edit it in the Text/hex editor in R-Studio.
You may then restore the partition to the hard drive using the R-Studio Copy module, although I'd rather test it on another disk until i'm sure that everything goes well.